The present invention relates to a magnetic head and, particularly, to a magnetic head using an amorphous magnetic alloy as a magnetic core.
Conventionally, an alloy material such as permalloy, sendust or the like or ferrite has been employed as a core material for use in a magnetic head. Among these materials, ferrite is the best with regard to wear resistance at present, but is inferior to the alloy material with regard to the problem of magnetic saturation of the head core material when used with a high density recording medium of high coercive force available in recent years, because the saturation magnetic-flux density B.sub.S is lower by 30 to 50% as compared with the alloy material. On the other hand, the alloy material is inferior in wear to the ferrite, but is superior in B.sub.S.
From the above point of view, an amorphous magnetic alloy, which is superior in both wear resistance and magnetic property, is interesting. Generally, it is difficult to form an amorphous magnetic alloy of sufficient thickness due to limitations of the manufacturing method, and thus a magnetic core is formed by a layer of such material having on both sides thereof non-magnetic substrates, thereby to ensure necessary mechanical strength thereof. Accordingly, the bonding of such substrates is extremely important.
In a ferrite magnetic head, glass bonding is normally used while with the alloy material, bonding is performed with the use of a silver-solder material, and operating temperatures therefore normally are 700.degree. C. or more. However, with an amorphous alloy it is necessary to operate normally at 500.degree. C. or lower, due to consideration of the magnetic characteristics because of the crystallization temperature (hereinafter referred to as Tx) of the material itself. Namely, if the amorphous magnetic alloy is adapted to heat at Tx or higher, the alloy is crystallized and becomes fragile, and simultaneously the magnetic characteristics become deteriorated so that the amorphous magnetic alloy cannot be used as the magnetic material. Accordingly, for the bonding of the head core material or the forming of the magnetic gap, with the use of the amorphous material it is desirable to use a so-called bonding agent such as ordinary epoxy resin or the like or to perform the bonding operation with the use of a soldering material. Although such procedures are safe in that the amorphous material is not crystallized, the resultant low bonding strength is disadvantageous because the operating temperature during these bonding operations is at most 300.degree. C. or lower.
An audio head formed in such manner has no serious problem, because the track width is wide and the magnetic gap length is wide. However, in a video tape recorder, a computer or a data recorder, it is difficult to maintain a precise width of the magnetic gap with such bonding or soldering material, because the track width is extremely small (for example, tens of micrometers) and the magnetic gap length is extremely small (for example, 0.3 micrometer or lower).
Accordingly, to maintain a magnetic gap of high precision, bonding with the use of glass is most reliable. However, when the magnetic head is constructed of the amorphous magnetic alloy, the performance of the bonding operation and the formation of the magnetic gap should be performed at 500.degree. C. or lower for the above-described reasons, and accordingly the glass material of low melting point of 500.degree. C. or less is required. Glass with such a low softening point contains a substantial amount of lead as such as PbO, and when such glass is employed for bonding to form the magnetic gap in a magnetic head, there is a disadvantage that the yield during operation is extremely low. It has been found that oxidizing, reducing reactions are caused between the PbO in the glass and the metal in the amorphous magnetic alloy at the interface between the amorphous magnetic alloy and the bonding glass, thus liberating metallic lead from inside the glass, thus resulting in considerable reduction of the bonding strength.